1. Field of the Invention
The present invention relates to a process of surface treating aluminum or aluminum alloy articles, and particularly to a process of surface treating aluminum or aluminum alloy articles which have been anodized.
2. Description of the Related Art
Articles made of aluminum or aluminum alloy are often anodized to form an oxide layer and subsequently colored to obtain decorative appearances.
Conventional processes for coloring surfaces of aluminum or aluminum alloy articles comprise color anodizing, adsorptive coloring and electrolytic coloring.
In color anodizing (integral method), aluminum or aluminum alloy articles are colored by finely divided inorganic dye particles which remain as an alloying constituent in oxide layers of the articles.
In adsorptive coloring, an organic dye is introduced into pores of an oxide layer of an aluminum or aluminum alloy article. The organic dye remains absorbed in a surface region of the oxide layer of the article.
Electrolytic coloring uses metal salt solutions to produce a colored oxide layer on the aluminum or aluminum alloy article. In a first process step of anodic oxidation, direct current is applied to aqueous sulfuric acid or other electrolyte solutions. In a second process step, the article is colored by applying alternating current to metal salt solutions. Metal particles are deposited at a bottom of pores in an oxide layer of the aluminum or aluminum alloy article.
Oxide layers on the aluminum or aluminum alloy articles are unstable and porous. The layers are liable to be degenerated by contact or by corrosive substances. In addition, such layers frequently also have an unattractive appearance. Furthermore, in adsorptive and electrolytic coloring, the obtained color easily fades due to lack of a protective layer on the colored surface.
In order to overcome the foregoing drawbacks, U.S. Pat. No. 4,648,911 discloses a process for sealing the surface of an anodized aluminum or aluminum alloy. The sealing process reduces the dimensions of the pores of the oxide layers on the surface of the aluminum or aluminum alloy, and thereby inhibits the aluminum or aluminum alloy from corroding or fading.
However, inhibition of corrosion or fading merely reduces the rate at which the oxide layer degenerates. The disclosed process does not completely or even thoroughly solve the aforementioned problems. Hence it is desired to provide a process of surface treating aluminum or aluminum alloy articles which can overcome the foregoing drawbacks of conventional processes.
A main object of the present invention is to provide a process of surface treating an aluminum or aluminum alloy article which prevents the article from being corroded.
Another object of the invention is to provide a process of surface treating an aluminum or aluminum alloy article which gives the article a long-lasting attractive appearance.
To achieve the above objects, a process of surface treating an aluminum or aluminum alloy article according to the present invention comprises the steps of: (1) forming an oxide layer on the aluminum or aluminum alloy article by anodizing; (2) sealing the oxide layer of the article; and (3) forming a protective film on the sealed oxide layer of the article.
The process may further comprise a step of coloring the oxide layer of the aluminum or aluminum alloy article between said steps (1) and (2).
The aluminum or aluminum alloy article is corrosion-resistant and resistant to damage by contact, by virtue of the protective film formed on the sealed oxide layer in said step (3). In addition, the protective film can also give the aluminum or aluminum alloy article a long-lasting attractive appearance by preventing a colored sealed oxide layer of the aluminum or aluminum alloy article from fading.
For the purpose of making the invention easier to understand, three embodiments thereof are described in detail herein, in which: